1. Field of the Invention
The present invention concerns the use of inkjet printer orifices which are coated with a continuous or discontinuous layer of titanium dioxide. The titanium dioxide acts as a catalyst at ambient pressure and temperature (optionally in the presence of light) to decompose excess ink components (solvents, etc.) to keep the inkjet nozzle free of excess ink and allowing for improved inkjet printing. Light irradiated TiO.sub.2 has an extremely small wetting angle of between about 0.0 to 1.0.degree..
2. Description of the Problem and Related Art
It is well known that when an inkjet printer is operated that drop trajectory and head/printer cleanliness problems develop due to uncontrolled orifice plate surface energy and/or wetting characteristics. This results in a buildup of ink or ink droplets on the print head which affects ink drop trajectory.
Various methods have been used to reduce or eliminate ink buildup have been used including coating the print head with a hydrophobic material to prevent ink head wetting and coating the print head with a varying alternating hydrophilic and hydrophilic coatings to essentially "pump" ink drops on the head away from the ink head orifice to clean the ink head area around the orifice. See for example, Takemoto et al. in U.S. Pat. No.5,387,440; and Hindagolla et al. in U.S. Pat. Nos. 5,434,606 and 5,595,785.
Orifice plates are mounted to ink-jet pens and include orifices through which ink drops are expelled by any one of a number of drop ejection systems. One such system is known as the thermal type and includes a thin-film resistor that is intermittently heated for vaporizing a portion of ink near an adjacent orifice. The rapid expansion of the vapor forces a drop of ink through the orifice. A partial vacuum or "back pressure" is maintained within the pen to keep ink from leaking out of the orifices when the drop ejection system is inactive.
There may be several orifices formed in a single orifice plate, each orifice having an associated drop ejection system for supplying a drop of ink on demand as the ink jet pen scans across a printing medium.
Some of the ink that is ejected through the orifice does not reach the printing medium (e.g., paper, polymer, etc.), and instead collects on the outer surface of the orifice plate (that is, the surface facing the printing medium). Some of this residual ink accumulates or puddles adjacent to the edge of the orifice and may alter the trajectory of the subsequently ejected drops, thereby reducing the overall quality of the printed image.
Residual ink on the outer surface of the orifice plate also tends to trap stray particles, such as paper fibers. The fibers may be held by the ink near the orifice to partially block the orifice and interfer with the ink drop ejections. Further, residual ink on the orifice plate outer surface may collect near the orifice into a thin sheet that is in fluid communication with ink stored in a supply chamber that is just inside the orifice. As a result, a continuous ink path between the chamber and the outer surface of the orifice plate may be formed. The path promotes ink leakage through the orifice. Accordingly, the outer surface of an inkjet pen orifice plate should be designed so that ink does not puddle in the vicinity of the orifice nor accumulate on the plate in an amount that may trap fibers and facilitates leakage as described above.
The inner surface of an orifice plate is exposed to the supply of ink. The ink flows over the inner surface to each orifice. Preferably, the inner surface of the orifice plate, including the portion defining the orifice, should facilitate the flow of ink from the supply through the orifice so that the drop ejection system receives a continuous and uniform flow of ink.
Additional references of interest include, for example:
A. Gonzalez-Martin et al. in U.S. Pat. No. 5,779,912 disclose a method and an apparatus for mineralizing organic contaminants in water or in air provides a photochemical oxidation in a unique two-phase or three-phase boundary system found in each pore of a TiO.sub.2 membrane in a photocatalytic reactor. PA1 D. J. Halko et al. U.S. Pat. No. 5,598,193 disclose a surface treatment with organic compounds to produce monolayers on an orifice plate for an inkjet printer. PA1 G. T. Hong, U.S. Pat. No. 5,545,337 describes a method of producing a layer of titanium dioxide on a surface using temperatures up to 700.degree. C. PA1 M. A. Anderson et al. in U.S. Pat. No. 5,137,604 disclose a reactor vessel using metal oxide (e.g. TiO.sub.2) ceramic membranes. PA1 S. L. Hindagolla et al. in U.S. Pat Nos. 5,434,606 and 5,595,785 disclose an orifice plate for an inkjet pen. PA1 B. J. Keefe et al. in U.S. Pat. No. 5,635,966 disclose an edge feed in a delivery thermal inkjet printhead structure and a method of fabrication. PA1 K. Takemoto et al. in U.S. Pat. No. 5,387,440 disclose a nozzle plate for an inkjet recording apparatus and method of preparing a nozzle plate. PA1 C. A. Schantz et al. in U.S. Pat. No. 5,305,015 disclose a laser ablated nozzle member of an inkjet printhead. PA1 S. T. Lam et al. in U.S. Pat. No. 4,773,971 disclose a reusable mandrel and a method of making the mandrel which has a substrate with a conductive film layer. PA1 R. Wong et al. Nature, Vol. 388, pp. 431-2 (Jul. 31, 1997). PA1 S. Strauss (1996) Technology Review, Vol. 99 (#2) pp. 23-25. PA1 I. Sopyan, et al. (1996) Journal of Electroanaytical Chemistry, Vol. 415, pp.183-186. PA1 C. D. Wheeler (October 1994) Soap-Cosmetics-Chemical Specialities, Vol. 70 (#10), P. 54(2). PA1 a plate having an inner surface and an outer surface wherein the inner surface portion defining an orifice that extends through the plate between the inner surface and the outer surface; PA1 the outer surface having a first outer surface portion surrounding the orifice, a second outer portion and a third outer surface portion surrounding the second outer surface portion, wherein the second surface portion is less wettable with respect to ink than the first outer surface portion and the third outer surface portion; and PA1 the orifice and outer surface joining to define an edge, said first outer surface portion being adjacent to the edge and separated from the orifice by the edge; PA1 wherein the first outer portion (and optionally the third outer portion) comprises a layer of titanium dioxide having a first wetting characteristic such that water and/or ink on the surface have a wetting characteristic and form a contact angle of between about 0 and 20.degree.. Optionally, the nonwetting surface and the wetting surface described are interchanged and this configuration also shows improved printing results. PA1 (a) utilizing the orifice plate for an inkjet pen described hereinabove having a surface coating of titanium dioxide; PA1 (b) decomposing catalytically water, organic dye, organic pigment, solvent or combinations thereof which contacts the titanium dioxide surface thereby self cleaning the titanium dioxide surface and reducing the misdirection of the ink. Optionally, the catalytic activity of the titanium dioxide layer is increased by contact with light.
Other references of general and specific interest include:
All articles, references, patents, applications, standards, etc. cited in this application are incorporated herein by reference in their entirety.
It would be useful to have a modified inkjet nozzle having a thin coating of titanium dioxide and a method with which there is improved printing on a medium. The present invention provides such an improved nozzle and an improved method.